This invention pertains to new compositions of matter comprising mixtures of bromotrifluoromethane and 1,1-difluoroethane which are useful as refrigerants, particularly as refrigerants in heat pumps.
In recent years, there has been an increase in the popularity of heat pumps to cool homes in the hot weather and to provide heat during the colder months. When a heat pump functions in a cooling mode, it operates on the same basic principle as does a conventional air-conditioner. Refrigerant is circulated through the system by a compressor, and it alternately absorbs and releases heat as it is vaporized and condensed in the course of its circulation around the circuit. Heat from the indoors is absorbed by the refrigerant as it vaporizes in the evaporator situated within the home or other space where cooling is desired, and this absorbed heat is ultimately released to the outside atmosphere when the refrigerant gas is compressed into the condenser which is in contact with the outside air. The absorbed heat is released as the refrigerant gas liquifies in the condenser. In the winter, a home or other type of building can be heated by reversing the flow of the refrigerant whereupon the condensor and evaporator switch roles. The coils that serve as a condenser and release heat in summer serve as the evaporator and the refrigerant absorbs heat from the outside atmosphere as it evaporates. This heat is then released indoors when the gas condenses. The most commonly used refrigerant for heat pumps is chlorodifluoromethane which is known in the industry as Refrigerant 22 or simply R-22.
One of the deficiencies in the performance of heat pumps for heating purposes is that they tend to lose their capacity to provide heat as the outside temperature gets colder. Because of the lower temperature at the evaporator the refrigerant will evaporate more slowly, and the less vaporization, the less absorption of heat for transfer to the indoors. In severe cold weather, the rate at which the refrigerant will vaporize in the outdoor evaporator will be low, and the compressor will consume disproportionately more electricity to compress the same amount of gas into the indoor condenser. Since heat pumps tend to lose capacity in this manner, they are used mostly in areas where winters are relatively mild, or they are used in conjunction with a supplementary heating system such as coal, oil or gas-fired heat or electrical resistance heating.
Various means have been suggested for minimizing the loss of capacity in a heat pump in colder weather. For example, a refrigerant having a relatively high vapor pressure will vaporize more readily than one with a lower vapor pressure, and thus the use of refrigerant with a higher vapor pressure in cold weather will facilitate vaporization. On the other hand, such a refrigerant can build up excessive pressure in the system in warmer weather when the pump is being used to cool. While it would be possible to employ a refrigerant with a relatively high vapor pressure in winter and then change to one with a lower vapor pressure in summer, this is not considered to be a convenient or practical solution to the problem. A similar but more convenient method of minimizing capacity fall off is suggested in U.S. Pat. No. 2,938,362 which employs a mixture of dichlorodifluoromethane (R-12) and bromotrifluoromethane (R-13Bl), a refrigerant known for its relatively high vapor pressure. According to the patent, this mixture is employed in a heat pump equipped with a reservoir and rectifying column which increases or decreases the proportion of R-13Bl in the active refrigerating circuit as the need arises. When a higher proportion of the refrigerant of higher vapor pressure is needed in the circuit to facilitate vaporization in the evaporator, an electrical heater in the reservoir and a valve mechanism are activated in response to decreased energy consumption by the compressor motor, due to decreasing capacity. In this way, refrigerant, enriched in R-13Bl which has a higher vapor pressure, is distilled through the rectifying column into the active refrigerating circuit. At the same time, an equal volume of the circulating refrigerant stream, which is less rich in the refrigerant of higher vapor pressure, enters the reservoir where it no longer participates in the refrigeration process. As a result of the introduction of additional R-13Bl, the pressure at the suction side of the compressor and thus the capacity of the system is increased over that which would prevail if the refrigerant mixture was not enriched in R-13Bl. When the pressure becomes too high as the temperature at the evaporator increases thus giving an increase in capacity beyond that needed, a control means responsive to increased energy consumption connects the active refrigerating circuit in series with the rectifying column and the reservoir, and the refrigerant mixture in these auxiliary devices is added to the circuit to provide an active refrigerating mixture no longer enriched in the refrigerant of higher vapor pressure.